The siphon effect has long been used to improve the waste discharge performance of flush toilets. Flush toilets of this type have an orifice formed in the outlet for inducing the siphon effect and a drain socket provided with a contraction that is used on the upstream side of the orifice (see, for example, JP-Hei 8-260551, pages 2-4 and FIG. 1). This drain socket produces a siphon effect at an early stage by producing a turbulent state of the flushing water at two stages, i.e., at the contracted portion on the upstream side and at the orifice of the outlet, thereby forming water curtains.
This drain socket forms water curtains by producing a turbulent state of the flushing water at two stages, i.e., at the contracted portion on the upstream side and at the orifice of the outlet, and further reduces the channel volume to produce a siphon effect at an early stage. As methods for enhancing floating waste suction and discharge efficiency at the final stage of siphoning, it has been proposed to increase the amount of channel flushing water by providing the inside of the channel of the drain socket with irregularities directed parallel to the floor or providing a reservoir chamber separately of the channel (see, for example, JP 2001-279796, pages 8-9 and FIG. 2-5).
Further, in the case where the position of the terminal outlet of the trap drainage channel of a flush toilet unit and the position of a drain pipe external of the toilet are not in alignment, it has been proposed to use a drain socket whose inlet and outlet are eccentrically positioned. This drain socket comprises a bent pipe member and a horizontal weir section provided at the outlet end thereof, and this horizontal weir section induces a siphon effect (see, for example, JP-Hei 8-326136, page 2 and FIGS. 2, 4).